borrowed neutral??

[pmac10]

can some of you installation guys enlighten me a little on borrowed neutrals?
i was changing a rcd socket outlet in the factory today which was spurred from a water metering control panel, switched the mcbs in the panel and the supply from dist. board, checked for dead, ok, but when the wires were diconnected from the old socket i found out the hard way, 230V appeared between neutral and earth?
could this be supplied from a lighting circuit? ideas please.

 

[pushrod]

Have noticed sparking neutrals myself. Have always assumed it to be the passage of electrons. (as opposed to charge).

electrons are charged

 

[GT1]

Yes they are. They are negatively charged.
What I meant to say was flow of electrons as opposed to voltage.

 

[SKY]

Sounds like he did follow safe isolation procedures, tested dead when shut down but then got a bolt from the natural to cpc/earth. That's the puzzle.

we are taught on the 2330 that safe isolation consists of testing:

between phase and neutral
between phase and earth
between neutral and earth.

(also the standard testing of the known and accurate device and using a proving unit)

 

[pmac10]

we are taught on the 2330 that safe isolation consists of testing:

between phase and neutral
between phase and earth
between neutral and earth.

(also the standard testing of the known and accurate device and using a proving unit)

as paul.m pointed out, i tested dead, which is what you describe as being taught in class, and this would still not have highlighted my painful experience. the voltage appeared after testing and only when neutral and earth where disconnected from their terminations, the very reason i'm asking for suggestions.

 

[jaresquire]

Just to clarify, pmac10, you killed the supply and found 230V between neutral and cpc when the rcd socket was dissed?

 

[pmac10]

jaresquire,that is correct, i also made and installed the panel a few years ago (utilising the supply from the old panel) so i know its wired proper and there is no polarity issues as the electronics wouldn't work.

 

[jaresquire]

Bit of a head scratcher, why were you changing the rcd socket - any other issues?

 

[pmac10]

water damage, couldn't reset the trip coil, have troubleshooted this panel in the past with no issues, if i get the time i'll figure it out, probably wont be til next time someone gets a blast, the joys of industry, thanks for all the replies.

 

[Marvo]

It's a long shot but is there a sneaky UPS incorrectly installed somewhere? You would usually hear a squealing noise though when the power goes off.

 

[pmac10]

all this 'borrowed neutral' discussion reignited my interest in a painful problem i experienced earlier this year, here i believe was the cause,Electrical Times - Features, second last paragraph, test for dead ok, disconnect conductors shock!:cuss:

 

[spark 68]

Back feed ?, ouch!

 

[pmac10]

Back feed ?, ouch!

indeed it was, i'm leaving this factory tomorrow after 5 years, and like a soppy c**t i'm worrying about the people replacing me:beatnik:

 

[VoltzElectrical]

Yes they are. They are negatively charged.
What I meant to say was flow of electrons as opposed to voltage.

electron flow (current) is only possible with voltage (electron push).